DC or AC electric power distribution systems using local voltage and current conversion circuits are increasingly being used in aerospace, military, industrial, transportation, and other industries. In these environments, solid state inverter circuits are used to locally convert voltage and current to required levels at application sites (e.g., an airframe). These inverter circuits commonly use capacitors for waveform shaping, for protection against electromagnetic interference (EMI), high-intensity radiated fields (HIRF) and lightning, and for other functional and protective functions. Capacitors may be included in both motor control units and inverter/converter units in the system, for example.
Many industries are increasing the use of commercial off-the-shelf (COTS) hardware to meet cost and replacement part availability goals. Although COTS hardware tends to be less expensive and more readily available than custom-made parts, COTS hardware also tends to have reduced lifespan and reliability. Thus, COTS hardware including capacitors, such as those used in inverter/converter applications, may experience occasional failures as they age.
When a capacitor fails, it can fail in either a shorted state or an open state. If the capacitor fails in a shorted state, current is allowed to flow freely through the system, potentially causing functional failure of electronic devices in the system. If the capacitor fails in an open state, it degrades or eliminates the protection offered by the capacitor and can cause other functional failures as well. Capacitor failures tend to be hard-failures; that is, they can occur without warning and cause the system to be inoperable until the capacitor is replaced. For example, if the capacitor stores energy used to start an engine, failure of that capacitor will make the engine unable to start. Other problems discovered only after the capacitor failure renders a system inoperable results in unplanned delays as the failed capacitor is replaced on an ad hoc basis. In other words, current systems do not contain any operating margins for capacitor failures.
There is a desire for a system that can anticipate capacitor failures before they cause functional failures in the system.